ALTAIR04-900TR Ver la hoja de datos (PDF) - STMicroelectronics
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ALTAIR04-900TR Datasheet PDF : 29 Pages
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ALTAIR04-900
Application information
Figure 15. Constant current operation: switching cycle waveforms
T
IP
t
Is
t
Q
t
IC
ICREF
t
ICREF
=
−
VC
R
5.6
Voltage feed-forward block
The current control structure uses the voltage VC to define the output current, according to
equation 2. Actually, the CC comparator is affected by Td an internal propagation delay,
which switches off the MOSFET with a peak current higher than the foreseen value.
This current overshoot is equal to:
Equation 3
∆ IP
=
VIN ⋅ Td
LP
where LP is the primary inductance and it introduces an error on the calculated CC set point,
depending on the input voltage.
The device implements a line feed-forward function, which solves the issue by introducing
an input offset voltage on the current sense signal, in order to adjust the cycle-by-cycle
current limitation.
The internal schematic is shown in Figure 16.
DocID18211 Rev 3
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